Draw roller for strip material

ABSTRACT

Draw rollers for striplike materials (especially paper or cardboard strips, plastic or metal foils), having a sheath ( 1 ) that can rotate around a fixed inner component, whereby said sheath is provided with air holes along the entire surface thereof, are already known per se. A vacuum chamber ( 8 ) is arranged in the winding area of the strip. Said vacuum chamber ( 8 ) can be subjected to an underpressure. According to the invention, another vacuum chamber ( 8 ) is arranged inside the sheath ( 1 ) in the running direction of said strip ( 2 ) directly in front of the vacuum chamber ( 8 ), whereby the underpressure in the second vacuum chamber is greater than the underpressure in the first vacuum chamber ( 8 ) and is independent thereof. The upstream second vacuum chamber ( 8 ) enables the separating layer of air adhering to the strip ( 2 ) to be suctioned in a targeted manner, whereby the contact surface of the strip ( 2 )/roller remains large enough to transmit high drawing forces.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US national phase of PCT applicationPCT/EP99/07075 filed Sep. 23, 1999 with a claim to the priority ofGerman patent application 19847799.6 itself filed Oct. 16, 1998.

FIELD OF THE INVENTION

The invention relates to a draw roller for strip or web-shapedmaterials, in particular for webs of paper or card-board or foils ofplastic or metal, which has a stationary inner part rotatably supportingan outer jacket that is formed over its entire surface with air holes.The interior of the jacket is subdivided into segment-like chambers fromwhich air is pumped in the region engaging the web. The subatmosphericpressure holds the web on the roller so as to increase the holdingstrength and thus transmit more tension to the web.

BACKGROUND OF THE INVENTION

Preferably such draw rollers are used in systems for making and/orfinishing web materials (webs of paper or card-board, foils of plasticor metal) in places where the workpiece can only be gripped on one side,for example because the other side has a layer of liquid coatingmaterial (German 1,474,973).

With high web-travel speeds the layer of air between the web and theroller creates problems as the web enters into contact with the roller.An air cushion is created between the web and the roller which holds upthe web and thus reduces the contact area. This reduction of the contactarea means that less tension can be transmitted. In extreme cases theroller rotates relative to the web.

OBJECT OF THE INVENTION

It is an object of the invention to improve on a draw roller of theabove-described type so that even at high web speeds large tensions canbe transmitted.

A second object of the invention is to provide a draw roller whosesurface can easily be adjusted for different web materials, speeds,and/or web widths.

SUMMARY OF THE INVENTION

This object is achieved in a draw roller for web-shaped materials, inparticular for webs of paper or cardboard or foils of plastic or metal,with a stationary inner part rotatably supporting an outer jacket thatis formed over its entire surface with air holes, and with a vacuumchamber maintained at subatmospheric pressure in a region of contactwith the web wherein inside the jacket relative to the travel directionof the web directly upstream of the vacuum chamber there is a furthervacuum chamber which is maintained at a subatmospheric pressureindependent of and greater than that of the chamber.

The upstream second;vacuum chamber makes it possible to eliminate theair trapped between the web and the roller so that the contact arearemains large in order to transmit the necessary tension.

The second object is achieved in a draw roller for web-shaped materialswith a stationary inner part rotatably supporting an outer jacket thatis formed over its entire surface with air holes, the inner part havingpartitions that subdivide the interior of the jacket into chambers ofwhich at least one chamber is connected to a vacuum line, and whereinthat the jacket is releasably mounted at both axial ends on annularrotatably supported bearing parts and can be released and drawn axiallyoff the inner part.

BRIEF DESCRIPTION OF THE DRAWING

The drawing serves for describing the invention with reference to asimplified illustrated embodiment.

FIG. 1 is a cross section through the draw roller;

FIG. 2 is a longitudinal section along the rotation axis;

FIG. 3 is an exploded view of the parts; and

FIG. 4 is a circuit diagram for the elements for setting the requiredpressure relationships in the individual chambers.

SPECIFIC DESCRIPTION

The draw roller according to the invention is used in systems for makingand/or finishing web-shaped materials (webs of paper or cardboard, foilsof metal or plastic) in order to move the web with a accurately definedhigh speed and/or to give it a predetermined tension while passingthrough treatment stations. Such stations serve for example for coating,impregnating, surfacing, or laminating or even for making plastic foils.They are used in all treatments in which the web can only be engaged onone side, for example downstream of applicators for coating materials,that is where the coated side cannot be touched. In these treatmentregions they serve as a master drive that sets an exact web-travel speedor even as a system for controlling web tension.

The draw roller has a jacket 1 which is rotatably driven and providedover its entire surface with throughgoing air holes. The porosity of thejacket 1 is created by a multiplicity of holes, by manufacture of aporous material, or the like. In addition the outer jacket surface canbe provided with a wear-resistant coating of rubber, ceramic, or thelike and/or one that increases the friction with the web 2. In order tomake air flow between the web 2 and the outer surface uniform and alsoto avoid marking the web 2, the jacket surface is preferably coveredwith a plastic or metal mesh. The jacket 1 has a very thin wall ofsteel, aluminum, or a fiber-reinforced plastic (GFK or GFK laminate) inorder to minimize its weight and inertia.

The interior of the jacket 1 is subdivided by radially extendingfull-length partitions 3, 4, 5, and 6 into chambers 7, 8, and 9 in eachof which a respective pressure can be set. The partitions 3, 4, 5, and 6are part of a normally stationary inner part and have on their radialouter ends friction-free seals 10 extending to the inner surface of thejacket 1. Preferably the inner part is comprised of a tube 11 extendingcoaxially to the roller axis A and on which the radially outwardlyprojecting partitions 3, 4, 5, and 6 are fixed and that is subdividedinternally into a corresponding number of distribution compartments 12,13, and 14 that communicate via openings or conduits 15, 16, and 17 withthe chambers 7, 8, and 9. The distribution compartments 12, 13, and 14are connected at one axial end of the tube 11 with respective vacuum orpressure lines 18, 19, and 20 (FIG. 4) in order to set in the chambers7, 8, and 9 the below-described pressure relationships. In addition theentire inner part is rotatable about the axis A in order to set theposition of the segment-shaped chambers 7, 8, and 9 relative to thecontact region with the web 2. Preferably this rotation of the innerpart is done by a motor M that is operated by a controller C. Thecontroller C positions the inner part according to a predeterminedalgorithm that takes into account particular physical characteristics ofthe web 2, for example its porosity, and certain operating parameters,for example the web travel speed.

In this embodiment the distribution chamber 14 is formed by an innertube 21 coaxial with the outer tube 11 and connected via the shortconduit 17 with the chamber 9. The chamber 14 is connected to thepressure line 20 while the distribution chambers 12 and 13 are connectedto the vacuum chambers 7 and 8 and to the vacuum lines 18 and 19. Thedistribution chambers 12 and 13 are formed between the outer tube 11 andthe inner tube 21 by partitions 22.

It is significant for the draw roller according to the invention that ithave two internal vacuum chambers 7 and 8 whose subatmospheric pressurescan be set independently of each other. The two vacuum chambers 7 and 8are arranged angularly on the roller immediately adjacent each otherrelative to the rotation direction D of the roller, the upstream vacuumchamber 7 having a greater subatmospheric pressure than the succeedingdownstream vacuum chamber 8 which is nonetheless still at subatmosphericpressure. The upstream vacuum chamber 7 has an angular dimension of atleast 10°, preferably 20° to 90°, and the downstream vacuum chamber 8has an angular dimension of at least 20°. Preferably the downstreamvacuum chamber 8 has a greater angular dimension than the upstreamvacuum chamber 7. The entire suction angle of the two vacuum chambers 7and 8 is at least as great as the contact angle with the web 2, which is30° to 240°.

In the preferred embodiment, following the downstream vacuum chamber 8inside the jacket 1 there is a pressure chamber 9 in which the pressureis superatmospheric. The openings in the jacket 1 in the region of thepressure chamber 9 emit air as a result of the overpressure to encourageseparation of the web 2 from the roller. The partition 5 between thevacuum chamber 8 and the pressure chamber 9 extends along an axial linewhere the web 2 should release from the roller. The interior of thejacket 1 is connected in a chamber 23 between the pressure chamber 9 andthe upstream vacuum chamber 7 neither to a pressure line nor to a vacuumline since this chamber 23 is not contacted by the web 2 and does notact on the web 2. At its ends the chamber 23 has throughgoing holes 35through which air leaks for pressure equalization with the surroundingatmosphere.

Before starting the draw roller the inner part with the partitions 3, 4,5, and 6 are set such that the upstream vacuum chamber 7 is in theregion in which the web 2 and the roller first contact each other.Preferably it is set such that the partition 4 between the two vacuumchambers 7 and 8 is at the desired initial-contact line. The downstreamvacuum chamber 8 is so constructed and set that it covers the entirecontact area of the web 2. Subsequently the pressure chamber 9 is in theregion where the web 2 leaves contact. In use the downstream vacuumchamber 8 in the contact region has a vacuum of between 1 KPa and 20 KPawhich depends on the sensitivity of the material and the web-travelspeed. In the upstream chamber 7 there is a stronger vacuum. Thepressure differential between the two chambers 7 and 8 is at least 0.5KPa, preferably 1 KPa to 10 KPa. The larger vacuum in the upstreamvacuum chamber 7 prevents air from getting trapped between the rollerand the web 2. Thus floating of the web 2 on a cushion of air andslipping between the web 2 and roller resulting from reduced contactarea is avoided. The thus increased contact area even at high web-travelspeeds at the vacuum chamber 8 makes it possible to transmitconsiderable tension. The independent adjustability of thesubatmospheric pressure in the vacuum chamber 7 makes it possible to setthis in accordance with web-travel speed so that constant tractionrelationships are set. Preferably the desired subatmospheric pressure inthe upstream chamber 7 is set depending on the web-travel speed and/orweb tension by the controller C automatically, for example by a controlvalve 39 in the feed line 18 for the vacuum chamber 7. Similarly it isadvantageously possible by turning the inner part to change the positionof the vacuum chamber 7 relative to the passing web 2 dependent on theweb-travel speed such that a maximum effective suction angle is set.

FIG. 2 is a longitudinal section transverse to the web-travel directionthrough a particularly advantageous embodiment of a draw rolleraccording to the invention. This construction makes it possible tochange the jacket very easily in order to accommodate the draw roller todifferent web materials and/or different web widths. Thus the jacket 1with the appropriate surface (rubber, ceramic, friction coating, etc)can be specially constructed with a particular air-hole array and/orspecial air-distributing structures (air-guide grooves, plastic or metalmeshes, etc) and/or various widths of suction area for the particularweb width.

The inner tube 21 and the outer tube 11 extend at the connection endaxially past the end of the jacket 1 and are rotatably mounted at theirprojecting end in the frame 27 of the machine. The inner tube 21 isthere connected to the compressed-air line 20 and the subdivided outertube 11 to the two vacuum lines 18 and 19. At the opposite driven endthe inner tube 21 has a plug or pin 24 closing the pressure chamber 14and supported by a radial bearing 25 inside a bearing part 26. Thebearing part 26 is rotatably mounted in a frame 27 of the apparatus bymeans of a radial bearing 28 and is connected via a torque-transmittingcoupling with a rotary drive 45. The end of the bearing part 26 turnedtoward the jacket 1 is screwed to the outer periphery of an annular endwall 29 whose outer diameter is the same as that of the jacket 1. Theend wall 29 is releasably bolted to the end of the jacket 1.

Inside the roller, pressure-tight regions at both axial ends are definedby respective annular seal walls 30 and 31 that are fixed to the innerpart and extend to an inner surface of the jacket 12. The sealing wall30 on the drive end is secured on the outside of the inner tube 1, thesealing wall 31 on the connection end is on the outside of the outertube 11. The sealing walls 30 and 31 are also connected in apressure-tight manner to axial ends of the partitions 3, 4, 5, and 6.The connection end has a bearing 32 rotatably supporting the jacket 1and having an inner race fixed on the outer tube 11. The outer race isfixed to an annular bearing part 33 over which a second annular end wall34 is fitted and to which it is releasably bolted. The annular end wall34 is secured to the connection end of the jacket 1. The end wall 34also has the throughgoing holes 37 that serve for pressure equalizationwith the outside in the region between it and the sealing wall 31 andthen via the holes 35 into the segment 32 and in the region between thesealing wall 30 and the end wall 29.

The above-described setting of the inner part comprised of the tubes 11and 21, the sealing walls 30 and 31, and the partitions 3, 4, 5, and 6not shown in FIG. 2 is done in that it is rotated on the bearings 25 and32 into the necessary position. When in use, the jacket 1 rotates on thetwo bearings 28 and 32. Changing of the jacket 1 can be done simply asshown in the exploded view of FIG. 3.

The jacket 1 is unbolted on the drive end from the end wall 29 and onthe connection end the end wall 34 from the bearing part 33. Then thejacket 1 with the end wall 34 is drawn off axially and switched with adifferently constructed jacket 1. The shape of the jacket 1 with theannular end wall 34 as replaceable part has the further advantage thatbefore installation bores can be drilled in the end wall to compensateout any throw.

FIG. 4 shows the schematic of the preferred apparatus by means of whichthe necessary pressure relationships are set in the vacuum chambers 7and 8 and in the pressure chamber 14. This apparatus needs only avariable-speed blower 38. Alternatively it is possible to connect eachvacuum or pressure chamber 7, 8, or 9 via conduits 18, 19, and 20 torespective suction or pressure ports of a blower.

In the embodiment according to FIG. 4 with only one blower 38, eachlow-pressure line 18 and 19 leading to a vacuum chamber 7 and 8 has arespective adjustable valve 39 or 40 by 15 means of which the necessarypressure in the respective vacuum chamber 7 or 8 can be adjusted.Upstream of the valves 39 and 49 the two vacuum lines 18 and 19 areconnected together to the intake of the blower 38. A line 41 connectedto the output of the blower 38 has another pressure-regulating valve 42vented to the outside through a muffler 43. Upstream of thepressure-regulating valve 42 is the connection to the pressure line 41that leads through a valve 44 to the pressure line 20 for the pressurechamber 9 in order to feed superatmospheric pressure to the pressurechamber 9. The circuit of FIG. 4 makes it possible to set individual andcontrollable pressures in each of the chamber 7, 8, and 14. Preferablysetting the pressure relationships in the individual chambers is doneautomatically by the controller C which operates the valves 39, 40, 42,and 44 dependent on the web-travel speed and/or the tension in the web.

What is claimed is:
 1. A draw roller for advancing a web, the rollerhaving: a generally nonrotatable inner part; a cylindrical jacket havinga surface centered on an axis, rotatable about the axis on the innerpart, and formed over substantially all of the surface with amultiplicity of air holes; drive means for rotating the jacket about theaxis in a rotational direction with the web engaging only a portion ofthe surface; partitions inside the jacket on the inner part formingagainst an inside face of the jacket an upstream vacuum chamberimmediately upstream in the direction from the web-engaging portion ofthe jacket, a pressure chamber immediately downstream in the directionfrom the web-engaging portion of the jacket, and a downstream vacuumchamber between the up-stream vacuum chamber and the pressure chamber;and blower means for creating subatmospheric pressures in the vacuumchambers with the pressure in the upstream chamber being substantiallyless than the pressure in the downstream vacuum chamber and for creatinga superatmospheric pressure in the pressure chamber, whereby air isevacuated from under the web as it engages the jacket, the web issolidly held by suction against the jacket where it engages the jacket,and the web is pushed by air off the jacket as it separates from thejacket.
 2. The draw roller defined in claim 1 wherein the subatmosphericpressure in the upstream vacuum chamber is at least 0.5 KPa greater thanthe subatmospheric pressure in the downstream vacuum chamber.
 3. Thedraw roller defined in claim 2 wherein the subatmospheric pressure inthe upstream vacuum chamber is between 1 KPa and 10 KPa greater than thesubatmospheric pressure in the downstream vacuum chamber.
 4. The drawroller defined in claim 1 wherein the upstream vacuum chamber has anangular dimension of at least 10°.
 5. The draw roller defined in claim 1wherein the downstream vacuum chamber has an angular dimension of atleast 30°.
 6. The draw roller defined in claim 1, further comprising: apair of annular rings at ends of the jacket; and means releasablysecuring the rings to the inner part.
 7. The draw roller defined inclaim 6 wherein the inner part includes an inner tube normallynonrotatable about the axis and having one end carrying one of the ringsand attached to the drive means and another end carrying the other ofthe rings and connected to the blower means.
 8. The draw roller definedin claim 7 wherein the inner part includes an outer tube coaxial withthe inner tube and having an end connected to the blower means, thetubes each being connected to a respective one of the chambers.
 9. Thedraw roller defined in claim 1 wherein the partitions form inside thejacket an ambient-pressure chamber upstream of the upstream chamber anddownstream of the pressure chamber, the ambient-pressure chamber beingvented to the atmosphere.
 10. The draw roller defined in claim 1 whereinthe blower means has an intake and an output and includes respectivepressure-regulating valves connecting the vacuum chambers to the intake,the output being connected to the pressure chamber.
 11. The draw rollerdefined in claim 1 further comprising control means connected to thedrive means for varying the subatmospheric pressure in the upstreamvacuum chamber in accordance with a peripheral speed of the jacket. 12.The draw roller defined in claim 1 further comprising means forlimitedly pivoting the inner part and partitions about the axis and forarresting the inner part and partitions in any of a multiplicity ofangularly offset positions.